The present invention relates to personnel or item management, or warehouse or transportation logistics, wherein electromagnetically interrogatable electronic coded labels attached to personnel or objects transmit data to or receive data from an interrogation system by means of electromagnetic waves.
Frequently such systems operate in regions in which other users of the electromagnetic spectrum also generate electromagnetic waves for related or unrelated purposes.
With increasing crowding of the electromagnetic spectrum, and a modern tendency of regulators to encourage re-use of spectrum by different users, there is generally a considerable amount of electromagnetic radiation in any region occupied by electronically coded labels. When used for communication, this radiation is often at a significant level to achieve long range, possibly in unfavorable propagation contexts, or to overcome noise. Although subject to regulation, this radiation is often at a particularly significant level close to its source. However, only a small part of such radiation reaches an intended receiver. Most is dissipated in objects other than the intended receiver or travels unimpeded to indefinitely far regions of space.
Passive electromagnetically interrogated electronically coded labels generally need to obtain their operating power from an electromagnetic wave. That power can come from a range of sources. Generally it is provided as an interrogation illumination signal specifically generated by an interrogator for this purpose.
However labels can be designed to receive operating power, either in whole or in part, from other sources such as the radiation first mentioned herein. This can be achieved without significant change to the power which those other sources provide to their intended receivers.
It is also true that such other sources can provide interfering signals to receivers of electronic label interrogators. With care, the operating frequency and waveforms of electronic label interrogators can be adjusted so that they combine with electromagnetic signals introduced for other purposes, to enhance the operating power available to electromagnetically interrogatable electronic coded labels. Alternatively or in addition, the signals from electronic label interrogators can be adjusted so as to avoid interference, within the receivers of such interrogators, to extraneous signal sources to which interrogator systems are exposed.
It would be particularly advantageous if both objectives could be simultaneously achieved. It will be shown herein that it is possible to do so.
An illustration of a multi-faceted electromagnetic communication situation is provided in FIG. 1, wherein a label interrogator 1 transmits through interrogation antenna 2, electromagnetic signals to a group of electronic coded labels 3 which may return information bearing reply signals to the interrogator through the same antenna 2 or a different antenna. The figure illustrates that transmitter 4 of a data link which operates in the vicinity of the interrogator may radiate, through data link antenna 5, an electromagnetic signal which may in part also illuminate the region occupied by labels 3.
The interrogator 1 of FIG. 1 may also be fitted with a signal sensing antenna 11 which assists the interrogator in its determination of what other electromagnetic signals may be present in its vicinity.
For precise control of signals generated by the interrogator 1 or the data link transmitter 4, the system may make use of a low noise oscillator or timing signal generator 6 conveying its signals to the signal sources 1 and 4 via connecting cables 7 and 8, or via electromagnetic waves launched by antenna 9.
In addition data or command signals may flow between the interrogator 1 and the data link 4 via signal path 10 which may be wired or electromagnetic.
Many principles of remote interrogation and programming of electromagnetically coded labels are described in the disclosures of PCT/AU90/00043, PCT/AU92/00143, PCT/AU92/00477, PCT/AU97/00428, PCT/AU98/00017, PCT/AU97/00385 and PCT/AU99/01165, the disclosures of which are incorporated herein by cross reference.
In operation of electronic label interrogation systems according to the prior art it is usual practice to seek to operate in regions of an electromagnetic spectrum unoccupied by other users. This is particularly true in systems which make use of passive labels, from which replies reaching a receiver are particularly weak as a result of two way propagation loss between interrogator and label, and energy conversion loss in the label.
In the prior art a principal factor which restricts interrogation range of a passive labelling system is a difficulty of developing, at a distance, sufficient radio frequency voltage at a rectifier element within the coded label for that rectifier to operate efficiently.
In the present invention, both limitations just mentioned are reduced when behaviour of the interrogator is adapted in relation to other electromagnetic propagation signals which may reach the coded labels or the interrogator receiver, so that label rectifier voltage is enhanced, or the interrogator receiver interfering signals are reduced.
Such adaptation may be possible because the interrogator may be supplied with information about other signals by being told characteristics of other signal sources in the region of an interrogator. Such characteristics may include: frequency; spectrum; power level; antenna positioning, orientation, and pattern; and frequency hopping if applicable. The interrogator may alternatively make its own measurements of adjacent extraneous electromagnetic fields.
An interrogator may share hardware with another system of independent function, for example there may be a common transmitting antenna between an interrogation system and the transmitter of a communication system.
There may be a common low-noise master oscillator when phase coherence between an interrogator transmitter signal and a transmitter signal of another system is important.
The interrogator signal may be arranged to form a particular spatial interference pattern with the transmitter signal of another system, or another signal from another antenna of the same or different interrogator. In such cases the phase and frequency relations between signals become important. The time for which coherent operation lasts also becomes important.
It may be advantageous to exploit fortuitous reflections from an object in creating useful interference patterns. Signals from an interrogator or from other systems may be reflected.
In frequency hopping systems, diagnosing and adopting the same hopping pattern, possibly with a frequency offset, as is being used by other systems, and using a phase coherent carrier, is a good way of ensuring a positive reinforcement of transmitter signals and simultaneous minimisation of interfering signals in the receiver. Such cooperating signals can be from two interrogators, or an interrogator and a communication system.